The investigators propose to develop a new catheter-tip measuring instrument which will allow minimally-invasive monitoring of lung capillary injury. The instrument will use ultrasonic and electrical impedance sensors to measure changes in blood protein and salt concentration seen in blood leaving the lungs, after the injection of normal and hypertonic saline into the blood entering the lung. It is hypothesized that the resulting osmotic fluid exchange and salt transport indicator curves can be interpreted to yield information on lung interstitial volume and the filtration and reflection coefficients for osmotic water extraction into the capillary blood space. The measurements will rely on the fact that blood protein concentration can be determined by measuring ultrasonic velocity, while hypertonic saline concentrations can be chosen which have sonic velocities identical to blood. Thus, sonic velocity changes in blood will, essentially, reflect water moving across the capillary barrier. Studies will be conducted to determine the effects of lung edema caused by increased venous blood pressure and capillary damage induced by oleic acid infusion into isolated perfused dog lungs, in order to evaluate the sensitivity of the method to these abnormalities and to compare parameters with related parameters stemming from radioisotope indicator-dilution studies. This research should provide the basis for a minimally-invasive clinical instrument relying on the injection of biocompatible material (saline) that will provide significant information for the monitoring of lung vascular function in patients with Acute Respiratory Distress Syndrome (ARDS) and related abnormalities.